Control of static electricity with polymeric beta-propiolactone



United States Patent Ofifice 2,715,592 Patented Aug. 16, 1955 CONTROL OF STATIC ELECTRICITY WITH POLY lVlERiC BETA-PROPIOLACTONE No Drawing. Application December 12, 1952, Serial No. 325,743

2 Claims. (Cl. 117-1395) (Granted under Title 35, U. S. Code (1952), see. 266) A non-exclusive, irrevocable, royalty-free license in the invention herein described, for all governmental purposes throughout the world, with the power to grant sublicenses for such purposes, is hereby granted to the Government of the United States of America.

This invention relates to the coating of wool with polymeric beta-propiolactone in order to decrease its ability to develop static electrical charges. This coating has the effect of increasing the surface conductivity of the wool or of increasing the ability of the wool to disperse charges to its surroundings, the net result being that the treated wool has a reduced ability to form electrostatic charges as compared with the untreated wool. The invention is primarily concerned with the coating of wool with beta-propiolactone polymer whereby to minimize the production of static electricity when the wool is subjected to various operations such as carding, winding, reeling, spinning, weaving, coating, sizing, and so forth. Further objects and advantages of this invention will be obvious from the description herein.

The development of static electricity is a problem that is encountered in numerous fields, for example in shipping inflammable liquids, in spraying paints and lacquers, in dry cleaning, and so forth. In the handling of wool as in carding, spinning, weaving and other mechanical operations, the problem of static electricity is very severe. The electrical charges cause the Wool fibers to cling to parts of machines causing interruption of machine operation and yarn breaks. In addition, the slivers, rovings, yarns, etc. emerge with a bearded, fuzzy appearance and objectionable liveliness. Various attempts have been made to control static electricity in handling of wool fibers. One technique widely employed is to keep the humidity of the mill near saturation. This moisturizing of the wool fiber helps a great deal but is not always satisfactory because many of the operations tend to dehydrate the wool fiber. Thus for example when wool is carded, the heat caused by friction tends to evaporate moisture from the wool whereby the wool is dehydrated to such a point that it tends to stick to the cards and otherwise interfere with normal operations. Another attack on the problem involves coating the wool fibers with various organic silicon compounds such as silicones. These compounds are effective to a great extent but due to their silicon content tend to exert an abrasive effect on metallic parts such as card wires, reels, etc.

It has now been found that if wool is coated with polymeric beta-propiolactone the problem of static electricity is overcome to a large extent. The lactone has the effect of reducing the charge on the wool produced when it is rubbed against a material such as iron. Thus for example when wool is coated with polymeric betapropiolactone, its position in the tiiboelectric series is lowered to a position between cotton and iron. This means that the amount of static electricity produced by friction of the wool against iron machinery parts is drastically reduced. For the purposes of illustrating this point the triboelectric series is reproduced below.

Positive Asbestos Glass Mica Wool

Cats fur Lead Silk Aluminum Paper, cotton Woods, iron Sealing wax Ebonite Ni, Cu, Ag, brass Sulphur Pt, Hg

India rubber Negative In this series each substance becomes positively charged if rubbed against any substance below it. Further, the greater the separation of the two substances in the table, the greater will be the tendency to create charge. It is thus apparent that if by application of polymeric betapropiolactone, the position of wool is moved close to iron then the charge produced by rubbing the treated wool against iron will be greatly reduced.

In applying our invention in practice, the wool is coated with beta-propiolactone polymer. The most convenient technique of coating the wool is to dissolve the polymer which is in general unreactive, in a volatile, inert solvent and apply this solution to the Wool. Application may involve dipping the wool in the solution, spraying the solution onto the wool, or applying the solution by other conventional apparatus such as rotating brushes, rollers, fountains, and so forth. In any event, it is preferable that the coating be uniform so that all parts of the wool are covered with about the same proportion of the polymer. Although acetone is the preferred solvent for forming a solution of the lactone polymer, other inert, volatile solvents may be used as for example, carbon tetrachloride, chloroform, ethylene dichloride, benzene, or light petroleum distillates. It is obvious that residual solvent may be removed from the coated wool by subjecting it to a current of air. If desired, the lactone polymer can be applied as a finely divided powder to the wool by the use of rotating brushes or other devices suitable for applying powders to materials.

The amount of beta-propiolactone polymer to be applied to the wool may be varied within Wide limits. In a general sense, the larger the proportion of lactone, the less will be the electrostatic charge formed on handling or contact with metallic objects. A significant decrease in ability to form a charge is obtained by treating with about 0.1% of the polymer, though usually more effective protection is obtained by raising this proportion to about 0.3%. Higher proportions may be used without any upper limit but as the proportion of lactone is raised above about 1% to 5%, each successive increase in proportion of lactone is not necessarily accompanied by a corresponding decrease in ability to form electrostatic charges.

The beta-propiolactone polymer coating can be removed if desired after mechanical processing. Thus for example when wool is coated with the beta-lactone polymer it may be desired to remove the coating after the mechanical operations of carding, spinning, weaving, etc. are accomplished and prior to bleaching or dyeing.

acid, sodium hydroxide, or ferric chloride.

In such case the wool may be washed with soap and wa'ter or other conventional laundering media.

If ap-' plication of water is undesirable the coating may also be washed with an inert, volatile solvent such as those mentioned above. In this connection it may be noted that itis conventional to wash woolens after weaving to remove. spinning oils, etc. Thus this washing will also serve to removethe beta-propiolactone polymer coating.

'It is to be noted that beta-propiolactone polymer may be obtained commercially. The polymer is made by subjecting the monomer to polymerization, catalyzed by acids, bases, and certain salts, as for example sulphuric By adding the beta-propiolactone to' the catalyst at a controlled rate,

' preferably in'solution in an inert solvent polymers of various chain lengths can be'obtained. Particularly useful polymers for the purposes of this invention are those which have an average molecular weight of about 800 to 1400 (about'10 to 20 propiolactone units) and which are solids melting at about 80 85 C. However, it is not essential to use these particular polymers and we can use any polymer which is a liquid or a solid and which is soluble in acetone or other inert solvent to the extent of at least about 1 to 10%.

The following example illustrates our invention in greater detail.

Example A'sample ofwool was immersed in an acetone solution of beta-propiolactone polymer (mol. wt. about 800), then drained and dried in air. The coated wool and a sample of the uncoated original wool were stored in an atmosphere of 65% relative humidity until their moisture con- .tent was at equilibrium. Both wool samples were then The surface charge on the carded wool was determined in' run through a lahoratory s'calejcarding machine.

each case by measuring (with a vacuum tube voltmeter) the degree to which the carded wool neutralized the charge on a condenser of known value and known charge.

Itwas found that the lactone-coated wool had a charge;

wool a solution of beta-propiolactone polymer dissolved in a volatile solvent, and evaporating residualsolvent from the thus treated woolto obtain wool coated with beta-propiolactone polymer.

References Cited-in the file of this patent UNlTED STATES PATENTS 2,361,036 Kung Oct. 24, 1944 2,487,885 Magofiin et al Nov. 15, 1949 2,517,573 Jones et a1. Aug. 8, 1950 2,672,397 Lundgren et al. Mar. 16, 1954 OTHER REFERENCES Fearnley et al., Jour Soc. Dyers and Colourers, March 1952, pages 88-91. 

1. IN A PROCESS WHEREIN WOOL IS SUBJECTED TO RUBBING CONTACT WITH A METAL OBJECT, THE IMPROVEMENT WHICH COMPRISES COATING THE WOOL WITH POLYMERIC BETA-PROPIOLACTONE PRIOR TO SUCH CONTACT WHEREBY TO REDUCE THE ABILITY OF THE WOOL TO FORM AND ELECTROSTATIC CHARGE. 